In the fabrication of integrated circuit devices, some processes developed depend on the conversion in resistivity of selected portions of a film of an insulator overlying a region to which low resistance electrical connections need to be made, for example, the source and drain regions of an MOS transistor. Such conversion avoids the need for removal of such portions of the insulating film, which removal may be difficult and which may leave openings which are difficult to penetrate reliably for making electrical connection to the underlying regions. One technique previously proposed has been to increase locally the conductivity of the film by the introduction of dopants so that electrical connection can be made to the local portion of the film avoiding the need for making an opening in the film. However, it proves difficult to dope films of insulating materials sufficiently to increase the conductivity to the desired level, because of limitations in available implantation apparatus and the tendency of the substrate to be affected by such heavy doping.